The objectives of this investigation are: (a) to continue to expand our knowledge of the physiology of the control of the resistance and capacitance functions of the various vascular beds, (b) to study the abnormal physiology of the control mechanisms in animal models of disease states such as hypotension, hemorrhage and shock, and (c) to extend these studies to man in states such as shock and the occlusive and vasospastic peripheral vascular diseases. It is hoped that such studies will lead to improved diagnosis and therapy of these states. The methods used to study the control of the resistance vessels will consist of measurements of blood flow and pressure in anesthetized animals and in unanesthetized animals using chronically implanted flow and pressure transducers, and of observations of the microcirculation. Control of capacitance vessels will be evaluated by measurements of blood flow and mean transit time using nondiffusible isotopes. In man, measurement of peripheral flow will involve registration of digital skin temperatures and measurement of digital blood flow by venous occlusion plethysmography. These measurements will be compared with the rate of heat elimination by conductive and evaporative heat transfer.